The present invention concerns a pulse wave generator for incorporation into cardiopulmonary bypass apparatus and extracorporeal membrane oxygenation apparatus, and apparatus that includes such a pulse wave generator.
Many complications following cardiopulmonary bypass (CPB) may be related to aberrant autonomic control of vascular function, which in turn may result from the lack of pulsatile perfusion pressures in most CPB circuits, leading to a loss of baroreceptor-mediated control and decrease in blood flow and oxygen delivery. Accordingly, it would be extremely desirable to provide CPB apparatus that provides both precise control of blood flow in a manner that mimics natural blood flow from the heart. Unfortunately, current apparatus falls short of these goals.
For example, U.S. Pat. No. 4,250,872 to Tamari discloses a cardiopulmonary bypass and extracorporeal oxygenation system comprising an oxygenator, a roller pump, and a pulse wave generator. The pulse wave generator is formed of a collapsible chamber, and is pneumatically driven. Thus the waveform of the output fluid from the pulse wave generator would be generally sinusoidal in nature, and would not accurately emulate the sharper peak waveform of the fluid output of the human heart.
U.S. Pat. No. 3,656,873 to Schiff discloses a pulsatile by-pass blood pump comprising a first xe2x80x9catriumxe2x80x9d chamber and a second xe2x80x9cventriclexe2x80x9d chamber which are said to be similar in design and function to corresponding portions of a natural heart. The ventricle chamber has a pair of flap valves on the inlet and outlet thereof. The atrium chamber serves as a buffer between the pulsatile operation of the ventricle, as well as the pressure within the inlet line by adjusting the size thereof. The atrium chamber does not serve as a pump. It would be difficult to precisely control the overall volume of blood flow with this type of pump.
In view of the foregoing, there is an ongoing need for cardiopulmonary bypass apparatus that incorporates a simple and convenient pulse wave generator that serves to mimic natural blood flow in the subject.
The present invention is a cardiopulmonary bypass and extracorporeal oxygenation apparatus that provides a pulsatile blood flow output. The apparatus comprises:
(a) a primary pump, which primary pump is preferably a continuous pump;
(b) an oxygenator in fluid communication with the primary pump;
(c) a pulse wave generator in fluid communication with the oxygenator and positioned downstream from the primary pump; the pulse wave generator comprises:
(i) a collapsible chamber having an inlet opening and an outlet opening formed therein;
(ii) a first one-way valve connected to the inlet opening and positioned to permit the flow of blood from the primary pump through the collapsible chamber; and
(d) a compression assembly operatively associated with the collapsible chamber and configured to alternately compress said collapsible chamber and permit the expansion of the collapsible chamber.
The use of a continuous pump feeding into a pulse chamber that is fitted with a one way valve provides unexpected advantages in the present invention. It would seem undesirable to pump blood with a continuous pump into one-way valve that would be closed during a portion of the pumping cycle (due to a relatively greater pressure in the pulse wave generator during the compression cycle thereof). This feature, however, creates a more rapid pressure transition (that is, a sharper pressure peak) in the pulsatile flow output of the pulse wave generator, rather than more sinusoidal pressure transitions created by prior art devices. Without wishing to be bound to any particular theory of the invention, the competing pressure fronts on the valves apparently cause them to open and close rapidly. The sharper pressure peaks created by the apparatus of the present invention are more like that of a natural heart, yet the present invention retains the advantage of control of volume of flow provided by a continuous pump.